General Chemistry Unit 14

A. Involves electron changes (can tell by change in charge) Cl NaBr 2NaCl + Br 2 B. Oxidation 1. First used to apply to reactions with oxygen (rusting, burning) 2. Now means loss of e- (charge becomes more +) 3. oxidation: 2Br - Br 2 + 2e- C. Reduction 1. First used to mean metal oxide ores “reduced” to the metals. 2. Now means gain of e- (charge becomes more -) 3. reduction: 2e- + Cl 2 2 Cl -

You can remember what happens to electrons by: 1. LEO the Lion says GER Losing Electrons is Oxidation; Gaining Electrons is Reduction 2. OIL RIG – Oxidation Is Loss of e-; Reduction Is Gain of e- LEO says GER OIL RIG

1. Assign charges 2. Find the element whose charge went up – this is the element oxidized. Connect the two with a line bracket going up. 3. Find the element whose charge went down – this is the element reduced. Connect the two with a line bracket going down. 4. Example (on board)

1. Free element = 0 (Na, Cu, Cl 2, H 2 ) 2. Monatomic ion is equal to charge on ion (Na + = +1) 3. H in compounds = +1 unless in a hydride (in LiH and other Group 1 hydrides the H = -1) 4. O in compounds = -2 unless in a peroxide (in H 2 O 2 the O = -1) 5. Sum charges equals the charge of the whole particle if not neutral (for NO 3 -, the charges add to -1, so the O = -2 as usual for a total of -6 on the 3 atoms of O. The N must be +5 to add to the ion’s charge of -1) 6. Group 1 = +1, Group 2 = +2, Group 13 = +3 in compounds Examples: (on board)

Car Battery A. 2 electrodes, Pb and PbO 2 as solid plates B. Concentrated H 2 SO 4 sulfuric acid acts as an electrolyte C. Reaction: Pb (s) + PbO 2(s) + 2 H 2 SO 4(aq) → 2PbSO 4(s) + 2H 2 O (l) Oxidation: Pb → Pb e - Reduction: Pb e - → Pb 2+ Pb is the RA, PbO 2 is the OA

A. Electrolytic conduction is the migration of e- (induced or forced by the current) B. The negative electrode is the cathode, the positive electrode is the anode. C. Positive ions are attracted to the cathode – called cations D. Negative ions are attracted to the anode – called anions E. Reduction occurs at the cathode, oxidation occurs at the anode (consonants/vowels) F. Electrolysis is a chemical change produced by an electrical current.

A. Energy (electricity) produced by a chemical process (spontaneous) 1. Dry cell – flashlight batteries (electrolyte paste inside - can be acid or base (alkaline)) 2. Lead storage cell – car battery (electrolyte solution inside – sulfuric acid) B. Cell shorthand notation – ABC (anode/bridge/cathode) 1. Anode written first: Oxidation shown with line between Zn|Zn Bridge: Double line represents salt bridge ║ 3. Cathode written last: Reduction shown with line between Cu 2+ |Cu 4. Overall: Zn|Zn 2+ ║ Cu 2+ |Cu C. Electrons flow from anode to cathode

Reducing Agent Oxidizing Agent e-e- e-e- e-e- e-e- e-e- e-e- AnodeCathode

* Electrons are produced (lost) at the anode * They travel through the wire to where you are powering or charging something (like your cell phone) * They arrive at the cathode where they reduce the cations * The anions flow through the salt bridge to the anode and the cations flow to the cathode to neutralize charge buildup.